1. Field of the Invention
The invention relates in general to pipe couplings, and more specifically to joints for coupling pipe sections such as used in hydraulic cylinders.
2. Description of the Prior Art
Hydraulic elevators use a jack unit which includes a plunger, and a cylinder made from steel pipe or steel tubing. When the required lift or vertical travel of the elevator exceeds approximately twenty feet, the cylinder is shipped to the job site in sections, which sections are then assembled to form the cylinder. It is conventional to weld an extension piece to one end of a cylinder section which includes a groove for an O-ring and external threads, and to weld an extension piece to one end of another cylinder section which includes a section having internal threads, and a section having a smooth bore for cooperating with the O-ring. The two sections must be very carefully vertically aligned with special tools to achieve and maintain alignment, and to provide adequate turning torque without distortion of the mating parts. If weight on the threads and lever forces due to whipping action of the top section are not carefully controlled, the joint will seize.